The present invention relates generally to the fields of transfer, injection and compression molding, and more particularly to the construction and physical characteristics of an insulation unit for interposition between a mold and an injection unit from which elastomeric stock can be expelled and transferred through the insulation unit to the mold. The term "injection unit" as used herein shall be understood to embrace injection and transfer assemblies alike as conventionally used in the art.
In particular, the present invention is an improvement over the insulation unit described and disclosed in United States Patent Application Ser. No. 316,165, filed on Dec. 18, 1972 now U.S. Pat. No. 3,859,024, issued Jan. 7, 1975, the subject matter of which is hereby incorporated by reference herein.
A number of difficulties have arisen with respect to the use of such an insulation unit. For example, when such an insulation unit is utilized in an environment in which there is employed a "bottomless" cylinder (a cylinder having an open end communicating directly with the insulation unit), upon retraction of the piston of the cylinder away from the insulation unit the elastomeric stock or compound interposed between the piston and the insulation unit tends to adhere to the insulation unit causing the latter to buckle at least slightly and crack eventually in the region of each of the sprue-communicating apertures formed in the insulation unit. It is, therefore, possible for the insulation unit to deteriorate more rapidly than necessary.
Another example of a difficulty associated with the use of such an insulation unit on a "bottomless" cylinder, and for that matter on a conventional "bottomed" transfer cylinder or pot (a cylinder or pot having a closed, multi-apertured, end upon which is superposed such as insulation unit), relates to the presence of undesirable constrictions at the interface of the insulation unit and mold, between the mold sprues and the insulation unit apertures. Such constrictions are presented when the mold sprues are not precisely coaxially aligned with their corresponding apertures formed in the insulation unit.
For example, after a given curing cycle, a mold operator removes the mold assembly from the region of the injection unit and empties the mold sprues and cavities. Since each of the mold sprues is extremely narrow in cross-section, it is difficult to restore the mold opposite the injection unit such that the mold sprues are in precise coaxial alignment with their corresponding apertures in the insulation unit. Failure to precisely re-align the mold sprues and insulation unit apertures results in the formation of constrictions at least partially blocking the mold sprues, respectively, and preventing the mold cavities from being effectively filled.
Still a further difficulty associated with the use of such an insulation unit involves the need, and heretofore inability, to effectively discharge or vent from the mold cavities undesirable gases collected in each of the mold cavities during the period in which they are filled with air or gas-pocketed elastomeric stock, and during the period in which the elastomeric stock cures and releases the gases in the mold cavities.